This invention relates to a fuel supply control method for internal combustion engines, and more particularly to a method of this kind which can adapt a fuel supply control system employing the method to a variety of engines and controls therefor having different operating characteristics.
A fuel supply control system adapted for use with an internal combustion engine, particularly a gasoline engine is widely known, which is adapted to determine the fuel injection period of a fuel injection device for control of the fuel injection quantity, i.e. the air/fuel ratio of an air/fuel mixture being supplied to the engine, by first determining a basic value of the above valve opening period as a function of engine rpm and intake pipe absolute pressure and then adding to and/or multiplying same by constants and/or coefficients being functions of engine rpm, intake pipe absolute pressure, engine temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., by electronic computing means.
According to this proposed fuel control system, while the engine is operating in a normal operating condition, the air/fuel ratio is controlled in feedback mode such that the valve opening period of the fuel injection device is controlled by varying the value of a coefficient in response to the output from an exhaust gas ingredient concentration detecting means which is arranged in the exhaust system of the engine, so as to attain a theoretical air/fuel ratio or a value close thereto (closed loop control), whereas while the engine is operating in one of particular operating conditions (e.g. an idling region, a mixture-leaning region, a wide-open-throttle region, and a fuel-cut effecting region), the air/fuel ratio is controlled in open loop mode by the use of a mean value of values of the above coefficient applied during the preceding feedback control, together with an exclusive coefficient corresponding to the kind of operating region in which the engine is then operating, thereby preventing any deviation of the air fuel ratio from a desired air/fuel ratio, and also achieving required air/fuel ratios best suited for the respective particular operating conditions, to thus reduce the fuel consumption as well as improve the driveability of the engine.
During the above open loop control, it is desirable that the air/fuel ratio should be accurately controlled to the predetermined air/fuel ratios best suited for the respective particular operating regions, by properly applying the respective exclusive coefficients and the mean value of the first-mentioned coefficient. However, there can occur variations in operating characteristics or performance between engines in different production lots, which can result in deviation of the actual air/fuel ratio from the predetermined ones. To eliminate such deviation, it is necessary to change or rewrite contents in a memory (e.g. a read-only memory) which is provided within an electronic control system applied, and stores various correction coefficients, correction variables, etc. required for the fuel supply control.
However, if the memory is a type which cannot be changed or rewritten in stored content, such as a mask ROM, the ROM per se has to be replaced with another one, and it is also necessary to add a change to the mask pattern used for manufacture of the mask ROM, which takes two or three months to have delivery of the new ROM and also requires a large cost.
Further, the deviation of the air fuel ratio from a desired air/fuel ratio can also be due to variations in the performance of various engine operating condition sensors and a system for controlling or driving the fuel injection device, etc. and/or due to aging changes in the performance of the sensors and the system. To adjust the sensors and the system for elimination of such deviation also takes a great deal of time and cost.
Besides, the air fuel ratio varies in different manners depending upon operating conditions of the engine, e.g. between a high engine rpm region and a low engine rpm region.